SLUAAT3 November   2023 TPS56837

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Why Soft Start is Needed
  5. 2Soft Start Principle
    1. 2.1 General Principle
    2. 2.2 Internal and External Soft Start
  6. 3Behaviors Related to Soft Start of TPS56837
    1. 3.1 Soft Start Sequence
    2. 3.2 Soft Start Discharge
    3. 3.3 UVP Hiccup Time
  7. 4How to Co-Lay TPS56837 and TPS56637
    1. 4.1 Pinout Differences of TPS56837 and TPS56637
    2. 4.2 Co-lay Guidance TPS56837 and TPS56637
  8. 5Summary
  9. 6References

3.3 UVP Hiccup Time

The TPS56837 has an under-voltage protection (UVP) feature. When the output voltage falls below 65% of the target voltage, the UVP comparator detects the under-voltage and shuts down the device after a deglitch time of 256 us, then re-starts after the hiccup time.

Figure 3-3 is the hiccup waveform of TPS56837 with an internal soft start capacitor Css. The figure shows that the hiccup time is 7 cycles of internal Css charge time. During hiccup, the Css is charged to 900 mV which is 1.5 x 600 mV (VREF) and then pulled up to internal VCC. So one cycle of internal Css charge time equals 1.5 x Tss. The total hiccup time is 7 x 1.5 x Tss, which is 10.5 cycles of Tss.

GUID-20231127-SS0I-TL9L-TSCT-JNWRJHBDKWCC-low.svgFigure 3-3 Hiccup Time with Internal Css

Figure 3-4 is the hiccup waveform of TPS56837 with an external 47-nF soft start capacitor Css. The hiccup time equals 7 cycles of Css charge time plus 8 cycles of Css discharge time. But the Css discharge time is not fixed. The discharge time changes with Css capacitance value and the biased status of Css.

GUID-20231121-SS0I-N338-KVNJ-3BGV9BFJDFXL-low.svgFigure 3-4 Hiccup Time With External Css = 47 nF